Method of production of anhydrous monofluorophosphoric acid



Patented Oct. 8, 1946 METHOD OF PRODUCTION OF ANHYDROUSMONOFLUOROPHOSPHORIC ACID Willy Lange, Cincinnati, Ohio, assignor, bydirect and mesne assignments, to Ozark Chemical Company, Tulsa, Okla, acorporationof Delaware No Drawing. Application June 28, 1944, Serial No.542,603

18 Claims. (01. 23-139) In an application for United States LettersPatent, Serial No. 478,838, filed March 11, 1943 by Ralph Livingston andme, jointly, anhydrous monofluorophosphoric acid (HzPOaF) and a methodof producing it from anhydrous hydrofluoric acid and water-freemetaphosphoric acid are described and claimed, but the production ofmetaphosphoric acid exactly corresponding to the formula H290: and freefrom its dehydration products for use in that method is accomplishedonly with a certain amount of difficulty. Thus a method for theproduction of monofluorophosphoric acid not requiring the use ofthe'somewhat difllcultly preparable metaphosphoric acid oilersadvantages over that disclosed in the said application.

Moreover anhydrous difluorophosphoric acid (HPOzFa) would be of distinctcommercial value if available to industry, but while a dilute aqueoussolution of this acid has been known for some' 20 time the solutioncannot be concentrated without complete hydrolysis of the acid. Theanhydrous form of this acid obtained as a lay-product in the hightemperature reaction between calcium fluoride and phosphorus pentcxidehas also been described in literature in recent years but the quantitiesof the acid obtainable in this way are so small'that the process is ofno interest as a possible commercial source of anhydrousdifluorophosphoric acid.

Earlier in the literature it has been, pointed out that in reacting a40% aqueous hydrofluoric acid solution and phosphorus pentcxide, theaque- A further object is to provide a method of producing the said acideither alone or in conjunction with anhydrous difluorophosphoric acid(HIPOzFz) which, after separation from the monofluorophosphoric acid,forms a valuble by-product.

A still further object is the provision of a method of the characteraforesaid which is capable of performance in such manner that none ofthe difluorophosphoric acid, substantially equal quantities of bothacids or, between these two extremes, any desired percentage ofdifluorophosphoric acid with relation to the monofluorophosticularlypointed out or will be apparent from ous solution of a mixture oforthophosphoric acid the following description.

This application is a continuation in-part of I my applications forUnited States Letters Patent, Serial Nos. 503,420 and 503,421, filedSeptember 22, 1943, in which, respectively, I described and claimed amethod of preparing substantially equal parts of monofluorophosphoricacid and difluorophosphoric acid through the reaction of phosphoruspentcxide with anhydrous hydrofluoric acid and subsequent distillationof the product fluoric acid of from about 69%-100% HF concentration, sothat by suitable selection of the degree of concentration and amount ofthe hydrofluoric acid, the method may be operated to supply either themonofluorophosphoric acid alone or the monofluorophosphoric and thedifluorophosphoric acids in a predetermined ratio 3 with consequentavoidance of production of an excess of difluorophosphoric acid in orderto meet commercial demand for the monofluorophosphoric acid.

More specifically, I have discovered that the reaction product obtainedat low temperatures in the violent reaction of phosphorus pentoxide withhydrofluoric acid of between about 69% and 100% inclusive HFconcentration and in a predetermined ratio is a liquid in which allthree fluorophosphoric acids (namely, mono-, diand hexafiuorophosphoricacids) and a fluorine-free phosphoric acid are present as can be shownby analytical methods described in the literature, but this liquid assuch cannot be used for commercial purposes so far as I am aware.However, if it be subjected to heat under conditions such that none ofthe gaseous reaction products are allowed to escape, a succession ofcomplicated intermediate reactions takes place, not presently known indetail, the end-product of which has a simple composition and is ofdefinite commercial interest, said end-product being in accordance withthe percentage concentration and relative quantity of the hydrofluoricacid employed either substantially pure monofluorophosphorio acid or amixture of the monofluorophosphoric and difluorophosphoric acids whichmay be readily separated by distillation, preferably under vacuum, thedifluorophosphoric acid passing oiT as the distillate and themonofluorophosphorlc acid remaining as the distillation residue, theyield of crude difluorophosphoric acid approaching the theoreticalvalue. Then if an analytically pure material is desired the crudedifluorophosphoric acid may be re-distilled under vacuum; the residualmonofluorophosphoricacid of the first distillation is of a technicalgrade and cannot be purified by further distillation.

The reaction between the phosphorus pentoxide and hydrofluoric acid ofabout 69% to 100% inclusive HF concentration to which reference has beenmade proceeds in accordance with the general equation in which X has anyvalue in the range from to l inclusive, and in the practice of theinvention care should be taken that during the reaction the phosphoruspentoxide, hydrogen fluoride and water, if any, always meet in the ratioof 1 mole P2O5:(2+X) moles HF:(1X) mole H2O in which X has any valuebetween 0 and 1 inclusive. By bearing this condition in mind one skilledin the art can readily calculate the quanitty of hydrofluoric acid of agiven HF concentration between about 69% and 100% inclusive which shouldbe used with a. certain quantity of phosphorus pentoxide in order toobtain the best results, as Well as the necessary concentration andquantity of the hydrofluoric acid required if it be desired to produceboth monofluorophosphoric and difluorophosphoric acids in a desiredratio. 1

However, to minimize the necessity for such calculations and tofacilitate the practice of my invention, I have set out in the followingtable the parts by weight of hydrofluoric acid of various HFconcentrations between about 69% and 100% inclusive which should be usedwith 100 parts by weight of phosphorus pentoxide. the value of X in thesaid equation in terms of moles and the resulting parts by weight ofacid or acids which in accordance with the invention are obtained(onccnlra Parts by Wight f fs i l l t tion of hy- Value of or-hydmmmricl y L L drofluoric X in ig g q g gfig figgg if 'g s by weight ofMonofluorozgf p phosphorus phosphoric g fi pcntoxide acid acid 68. 97 0.00 40. 84 140. 84 O. 00 69. 00 0. 001074 40. 140. 77 0. 08 70. 00 0.03226 40. 89 138. 57 2. 32 71. 00 0. 06350 40. 93 136. 37 4. 56 72. 00 009483 40. 98 134. 17 6. 81 73. 00 0. 1262 41. 02 131. 96 9. 06 74. 00 0.1577 41. 07 129. 74 ll. 33 75. 00 0. 1892 41. 11 127. 52 13. 59 76. 000. 2208 41. 16 125. 29 15. 87 77. 00 0. 2524 41. 20 123. 07 18. 13 78.00 0. 2852 41. 25 120. 76 20. 49 79. 00 0. 3159 41. 29 118. 60 22. 6980. 00 0. 3478 41. 34 116. 35 24. 99 81. 00 0. 3797 41. 38 114. 11 27.27 82. 00 0. 4118 41. 43 111. 85 29. 58 83. 00 0. 4438 41. 47 109. 5931. 88 84. U0 0. 4760 41. 52 107. 32 34. 20 85. 00 0. 5082 41. 56 105.06 36. 50 86. 00 0. 5405 41. 61 102. 78 38. 83 87. 00 0. 5728 41. 65100. 50 41. 15 88. 00 O. 6053 41. 70 98. 22 43. 48 89. 00 0. 6378 41. 7495. 93 45. 81 90. 00 0. 6703 41. 79 93. 64 48. 15 91. 00 0. 7030 41. 8491. 34 50. 50 92. 00 0. 7357 41. 88 89. 03 52. 85 93. 00 0. 7685 41. 9386. 73 55. 2O 94. 00 0. 8013 41. 97 84. 41 57. 56 95. 00 0. 8342 42.0282. 10 59. 92 96. 00 0. 8673 42. 06 79. 77 62. 30 97. 00 0. 9003 42. 1177. 44 64. 67 98. 00 0. 9335 42. 16 75. 11 67. 05 99. 00 0. 9667 42. 2072. 76 69. 44 100. 00 1. 0000 42. 25 70. 42 71. 83

It will be apparent from this table that when operating withhydrofluoric acid of 68.97% concentration no difluorophosphoric acid isproduced; that when operating with hydrofluoric acid of substantially100% concentration approximately equal quantities ofmonofluorophosphoric and difluorophosphoric acids are produced and thatbetween these two extremes progressively greater amounts of thedifluorophosphoric acid are produced as the concentration of thehydrofluoric acid increases.

The temperature at which the reaction is performed mayvary from very lowones to those exceeding the boiling point of hydrofluoric acid of 100%concentration but at temperatures exceeding the boiling point of lowboiling reaction products, the reaction should be carried out in aclosed system, with or without pressure, in order to avoid losses ofhydrofluoric acid and of gaseous reaction products, the presence ofwhich are necessary to secure an end-product consisting essentially ofmonofluorophosphoric acid or of monofluorophosphoric anddifluorophosphoric acids.

For attainment of optimum results and products of essential purity theproportions of ingredients employed when operating with hydrofluoricacid of any given HF concentration within the ranges specified must becarefully followed in accordance with the foregoing table, as departurestherefrom may result in roduction of impure difluorophosphoric aciddistillates and/or fluorine-free phosphoric acid instead of distillationresidues consisting only of monofluorophosphoric acid, and it is ofutmost importance that none of the products incident to the reactionbetween the phosphorus pentoxide and hydrofluoric acid be permitted toescape from the reaction vessel. To this end the reaction may be carriedout in a closed vesselof suitable type, or a vessel having a refluxcondenser associated therewith whereby all gases and vapors developedduring the reaction are returned by condensation or, in fact, by anymeans suitable for attainment of the desired end.

In the practice of the invention the reaction of the phosphoruspentoxide and the hydrofluoric acid may be eflected in various ways.Thus the phosphorus pentoxide may be added in small portions, a plyinagitation, to liquid hydrofluoric acid maintained at such lowtemperature that the reaction products, gaseous at room temperature,remain dissolved in the liquid reaction product at ordinary pressure.Or, if preferred, hydrofluoric acid may be passed into a closed,evacuated, rotating cylindrical and suitably cooled container holdingthe phosphorus pentoxide so that hydrogen fluoride and low boilingreaction products are condensed, or the hydrofluoric and may be passedinto a closed, evacuated container holdin: the phosphorus pentoxide,applying pressure, or the phosphorus pentoxide with air as the carriergas may be blown into a stream of evaporated hydrofluoric acid in suchmanner that the phosphorus pentoxide and hydrogen fluoride always meetin a ratio of 1 mol P205: (2+1!) moles HF:(1-x) mole H:O,.if any, wherex has any value in the range from 0 to 1 inclusive and all reactionproducts are conserved.

If a reaction temperature of lower than about 150 C. has been utilized,it is generally necessary to keep the reaction product in a closedcontainer at an elevated temperature for a time suiflcient to enable theabove mentioned intermediate reactions to come to completion, the rateof these reactions depending upon the temperature. The time andtemperature of this treatment may vary although generally a temperatureof irom about 90 C. to 150 C. and a time of from 2 to 12 hours isrequired. It will be understood, however, that the time and temperaturejust mentioned are by way of example only and not by way of limitationsince other times and temperatures may be employed with equal facilityand, further, that it the reaction of the phosphorus pentoxide with thehydrofluoric acid has taken place at temperature above about 150 C.usually no after treat-v ment as just described is necessary since theintermediate reactions may have already taken place to greater or lesserextent.

It will be appreciated that the excess of water in hydrofluoric acids ofless than about 69% HF is inimical to success of the method andattainment of the desired ends since when such acids are used themonofluorophosphoric acid produced is associated with fluorine-freephosphoric acid which cannot be separated from it.

The following are illustrative of difierent ways of practising themethod of the invention in accordance with the general equation inwhich'X has any value in the range from 0 to 1 inclusive:

Example 1.58 parts by weight of aqueous hydrofluoric acid of about 69%HF are placed in a platinum bottle and cooled with a mixture of solidcarbon dioxide and alcohol and 142 parts by weight of phosphoruspentoxide are added in small portions under agitation so that thetemperature of the liquid does not rise substantially. The phosphoruspentoxide reacts vigorously with the aqueous hydrofluoric acid'anddissolves quickly and after all the phosphorus pentoxide has been addedto the acid a clear liquid is obtained. The bottle is then closed andheated for ten hours at 6 C. only slight pressure being developed duringthis operation. The resulting reaction product is anhydrousmonofluorophosphoric acid which exhibits all analytical data andidentifying characteristics described in said application, Be-

rial No. 478,838. It cannot be purified by distillation.

Example 2.142 parts (by weight of phosphorus pentoxide are placed in aclosed, jacketed, stainless steel mixer having two constantly rotatingcurved blades, and'oil is circulated through the jacket. After themixerhas been evacuated aqueous hydrofluoric acid of about 69% HF is runinto the mixer, later applying pressure, and by cooling the circulatingoil and regulating the rate of introduction'of the acid a temperature ofabout C. is maintained in the mixer. After 58 parts by weight of theacid have been introduced the reaction product is allowed to slowly cooldown to room temperature during a period of approximately 3 hours. Theflnal product again is anhydrous monofluorophosphoric acid.

,Since in these examples hydrofluoric acid or a concentration of about69% HF is employed, the value of x in the general equation is 0 and itis thus simplified to PaOs+2HF+HaO=2KzPOzE no difluorophosphoric acidbeing produced.

At this point it may be observed that an aqueous hydrofluoric acid ofapproximately 69% 81" concentration contains the acid and water in aratio of 2 moles HF:1 mole H20, thus conforming to the general equationwhen X equals 0.

The following are illustrative of the practice of the method where amore concentrated aqueous hydrofluoric acid is used:

Ezanwle 3.--58.5 parts by weight of aqueous hydrofluoric acid of 77.43%HF are placed in a platinum bottle and cooled with a mixture orsolidcaroperation. The resulting reaction product is a mixture ofmonofluorophosphoric acid and difluorophosphoric acid and is subjectedto distillation at a pressure of 50 mm. of mercury to separate theacids, the temperature of the batch being slowly raised to 150 C. butnot higher. The vapors of difluorophosphoric acid evolved during thedistillation are condensed by passing through a condenser cooled withbrine of -20 C. and a yield of 176.2 parts by weight ofmonofluorophosphoric acid'is obtained and 24.2 parts of crudedifluorophosphoric acid. To further purify it, the difluorophosphoricacid may be re-distiiled at a pressure of 200 mm. of mercury at whichpressure it boils at about 70 C. It will be noted that in the reactionthe components are used in the ratio of i mole PzO5:(2+X) moles HF:(1-X)mole H2O.

Example 4.59.0 parts by weight of aqueous hydrofluoric acid of 84.95% HFare combined with 142 parts by weight of phosphorus pentoxide in themanner described in Example 3 and the reaction product subjected to liketreatment and subsequent distillation to separate the difluorophosphoricacid from the monofluorophosphoric acid. A yield of 150.9 parts byweight of the latter and 50.5 parts of the former is obtained and itwill'be noted that the components are 8 19- plied in the same ratio asin Example 3 but with X accorded a dlflerent value.

Example 5.-59.5 parts by weight of aqueous hydrofluoric acid of. 91.78%HF are combined with 142 parts by weight of phosphorus pentoxide and theresultant product again treated as in Example 3. Components are thussupplied in the same ratio as in Examples 3 and 4 though again with asuitably different value for X, but because of the higher concentrationof the hydrofluoric acid a yield of 128.3 parts by weight ofmonofluorophosphoric acid and 73.9 parts of difluorophosphoric acid isobtained after the distillation step.

In the three last examples the value of X in the general equation isintermediate between and 1, having the lowest value in Eample 3 andprogressively higher values in the others.

The following are illustrative of the practice of the method wherehydrofluoric acid of a concentration of 100% HF is utilized, i. e., theanhydrous form of the acid, and as under these conditions the value of Xin the general equation is 1, it is correspondingly simplified to and ineach instance a yield approximating the theoretical yield ofmonofluorophosphoric and difluorophosphoric acids respectively as setforth in the foregoing table is obtained.

Example 6.60 parts by weight of anhydrous hydrogen fluoride are placedin a platinum bottle and cooled to the temperature of a mixture of solidcarbon dioxide and alcohol. 142 parts by weight of phosphorus pentoxidearethen added in small portions under agitation so that the temperatureof the liquid does not rise appreciably. It will be-noted that in thereaction the components are used in the ratio of 1 mole P205113 molesHF. The phosphorus pentoxide reacts vigorously with the hydrogenfluoride and dissolves quickly and after all of it has been added to theacid a clear liquid is obtained. The bottle is then closed and heatedfor 8 hours at 85 C., only slight pressure being developed during thisoperation. The resulting reaction product is a mixture ofdifiuorophosphoric and monofluorophosphoric acids and is subjected todistillation at a pressure of 50 mm. of mercury to separate the formerfrom the latter, the temperature of the batch being slowly raised to 150C. but not higher. The vapors of difluorophosphoric acid evolved duringthe distillation are condensed by passing through a condenser cooledwith a brine of -20 C. and a yield of 97 parts by weight of crudedifluorophosphoric acid is obtained and 103 parts of crudemonofluorophosphoric acid. To further purify it the difluorophosphoricacid may be re-distilled as in Example 3. This purifled product whenanalyzed by analytical methods established in the literature is found tocontain P 30.6%; F 37.0% as against the calculated values respectivelyof P 30.4% and F 37.2%. The monofluorophosphoric acid is obtained as adistillation residue and is found to contain when likewise suitablyanalyzed P 30.7% F 20.1% as against the calculated values respectivelyof P 31.7% andF 19.0%.

Example 7.l42 parts by weight of phosphorus pentoxide are placed in a,closed jacketed stainless steel mixer having two constantly rotatingcurved blades and cooled with a brine of -20 C. circulating through thejacket. The mixer is then evacuated and anhydrous hydrogen fluorideslowly passed into it, in the latest stage applying pressure. Afterparts by weight of the fluoride have been introduced, the mixer inletvalve is closed and the mixer warmed up slowly to a final temperature of90 C. and maintained there for 5 hours. The reaction product afterdistillation in the manner described in Example 6 affords a yield of 96parts by weight of crude difluorophosphoric acid and a distillationresidue of (:04 parts by weight of monofluorophosphoric aei Example8.'142 parts by weight of phosphorus pentoxide are placed in a mixersimilar to that described in Example 7 and oil is circulated through itsjacket. After the mixer has been evacuated anhydrous hydrogen fluorideis passed into it applying pressure. By suitable cooling of thecirculating oil and regulation of the rate of introduction of thehydrogen fluoride into the mixer, a temperature of about-150 C. ismaintained in the latter. After 60 parts by weight of the fluoride havebeen introduced, the mixer inlet valve is closed and the reactionproduct allowed to slowly cool down to room temperature for a period ofapproximately three hours. By

like distillation of this product, a yield of 91 parts by weight ofdifluorophosphoric acid and 109 parts of monofluorophosphoric acid isobtained.

All the foregoing examples numbered 1 to 8 inclusive are given by way ofillustration only and not in any restrictive or limiting sense since itwill be understood from the foregoing description of the invention thatso long as phosphorus pentoxide and the proper quantity of hydrofluoricacid of suitable HF concentration are mixed in the ratio of 1 mole P205:(2+X) moles HE: (1-X) mole H20 where X has any value in the range from 0to 1 inclusive, with after treatment by heating the reaction product ina closed container or its equivalent if the reaction has not gone tocompletion according to the equation in which X has any value in therange from 0 to 1 inclusive, many other ways may be employed forcombining and subsequently treating the initially supplied components inorder to conform to special requirements of the equipment beingutilized, the form in which the phosphorus plated therewith and,according to the conditions of the reaction, ordinary or pressurevessels may be used. The practice of the invention therefore does notrequire specially constructed apparatus and as substantially purephosphorus pentoxide and hydrofluoric acid may be obtained withoutdifliculty in the open market the invention readily lends itself tocommercial usage.

It will now be apparent that practice of the method may be readilyadjusted from time to time to conform to market demand for the acids orfor other reasons without change in the equipment employed. Thus, forexample, if during a certain period the said demand approximates 7 tonsof the monofluorophosphoric acid to 3 tons of the difluorophosphoricacid, the method may be operated to produce both acids in approximatelythat ratio, or should demand for the difluorophosphoric acid" becomenegligible it may be operated to produce the monofluorophosphoric acidalone, a feature of the invention which is obviously of great importanceto manufacturers oi these acids. Thus my invention for the first time,as far as, I amaware. makes possible the production of anhydrousmonofluorophosphoric acid, as well as anhydrous horicacid suitable forindustrial purposes. from readily available materials in a convenientand commercially practical way.

Concerning some of the properties of these acids, it may be mentionedthat anhydrous monofluorophosphoric acid HzPOaF exhibits to a decideddegree some of thechemical properties of concentrated sulfuric acidwithout showing any oxidizing action and anhydrous difluorophosphoricacid HPOaFz, resembles to some extent anhydrous perchloric acidwithoutany oxidizing or explosive properties. In addition to having anumber of properties of a non-oxidising pseudosulfuric acid HzPOsF and anon-explosive, nonoxidizing "pseudo-perchloric acid HPOzFa, both acidsare derivatives of hydrogen fluorideas well as of orthophosphoric acid,and they combine in a convenient form the reactivities of both anhydrousorthophosphoric acid and anhydrous hydrogen fluoride for a number ofreactions.

The salts of both monofluorophosphoric and diiluorophosphoric acids havebeen described in the literature. They may be produced now on acommercial scale by passing calculated quantities of the anhydrous acidsin a thin stream into aqueous solutions of alkali bases or aqueoussuspensions of non-alkali bases undergoing stirring and kept at a lowtemperature, and then by evaporating the water in good vacuo at a lowtemperature to avoid hydrolysis. Or dry amines, like anhydrous ammonia,methylamine, aniline, pyridine, are reacted in the theoreticallyrequired quantities with the strongly cooled acids. or special interestare the aniline salts, which may be transformed into the dlazoniumcompounds which, in turn, .when heated in the absence or water, willform the corresponding aryl fluorophosphates with loss of theirnitrogen.

The anhydrous fluorophosphoric acids may be used as catalysts forpolymerization, condensation and alkylation reactions, especially forcombining such compounds as isoalkanes an'd oleflnes or lsooleflnes.Esters may be prepared by reacting oleflnic or acetylenic compounds withthe anhydrous acids in the presence of catalysts, or by reactingalcohols or ethers with the anhydrous acids. 01 special interest are theesters of monofluorophosphoric acid. Their similarity with thecorresponding sulfuric acid derivatives is farreaching. The long-chainmonoalkyl-(and isoalkyl) monofluorophosphoric acid salts, such as sodiumlauryl mdnofluorophosphate, are surfaceactive agents.Monoethyl-monofluorophosphoric acid, obtained e. gQby reacting theanhydrous acid with ethylene, forms diethyl monofluorophosphate in areaction corresponding to that of monoethyl sulfuric acid which, whenheated, forms diethyl sulfate.

Due to their non-oxidizing nature, both said fluorophosphoric acids maybe used as anhydrous acids in the non-oxidizing refining of oils and thelike, while other uses in addition to those just suggested may bereadily devised and other compounds may be prepared from them by thoseskilled in the art.

Having thus described my invention, I claim in which x has any value inthe range from 0 to 1 inclusive, and maintaining the mixture in thepresence of heat and under conditions prevent ing the escape of anyproducts of the reaction until the latter goes to completion accordingto said equation.

2. In a method of producing anhydrous monofluorophosphoric acid, thesteps of mixing phosphorus pentoxide and hydrofluoric acid or any HFconcentration between about 69% and inclusive according to the equationin which X has any value in the range from 0 to 1 inclusive, and heatingwhile preventing escape of the reaction products until the reaction hasgone to completion according to said equation. 3. In a method ofproducing anhydrous monofluorophosphoric acid, the steps of mixingphosphorus pentoxide and hydrofluoric acid of any HF concentration fromabout 69% to 100% inclusive in the ratio of 1 mole P2Os:(2+x) molesHF:(1X) mole H2O where X has any value in the range from 0 to 1inclusive, and then heating the product in a closed vessel at atemperature not exceeding about C'. until the reaction has gone tocompletion according to the equation in which X represents any numberbetween 0 and 1 inclusive.

4. The method of producing anhydrous monofluorophosphoric acid whichincludes the steps of mixing phosphorus pentoxide and a hydrofluoricacid of concentration exceeding 69% H1 substantially according to theequation in which X has any value in the range from 0 to 1 inclusive,maintaining the mixture in a closed container at a temperaturesuflicient to cause the reaction to go to completion according to saidequation and thereby form a resultant product containingmonofluorophosphoric and difluorophosphoric acids, and then separatingthe difluorophosphoric acid in vapor form from the monofluorophosphoricacid by distillation.

5. The method of producing anhydrous monofluorophosphoric acid whichincludes the steps of mixing phosphorus pentoxide and a hydrofluoricacid of a concentration of from 69% to 100% inclusive HF in the ratio of1 mole P20s2(2-|-X) moles HF: (1-X) mole H2O in which X has any valuefrom 0 up to and including 1, maintaining the ingredients in a closedvessel until completion of the reaction among them substantiallyaccording to the equation in which X has any value in the range from 0to 1 inclusive to thereby form a resultant product containingmonofluorophosphoric and difluorophosphoric acids, and thenseparatingsaid acids by distillation.

6. The method of producing anhydrous monofluorophosphoric acid whichcomprises combining phosphorus pentoxide and hydrofluoric acid of HFconcentration exceeding 69% substantially according to the equation inwhich X has any value in the range from to 1 inclusive, maintaining thereaction products in a closed vessel at a temperature and for a timesuflicient to cause the reaction to go to completion according to saidequation, and then separating the monofluorophosphoric anddifluorophosphoric acids in the resultant product b distillation.

7. The method of producing anhydrous monofiuorophosphoric acid whichcomprises mixing phosphorus pentoxide and hydrofluoric acid of about 69%HF in the ratio of 1 mole P205Z2 moles HF:1 mole H20, and thenmaintaining the reaction product in a closed vessel at a temperature andfor a time suflicient to cause the reaction to go to completionaccording to the equation P2O5+2HF+H2O=2H2PO3R 8. In a method ofproducing anhydrous monofiuorophosphoric acid, the steps of mixingphosphorus pentoxide and hydrofluoric acid of any I-IF' concentrationfrom about 69% to 100% inclusive in the ratio of 1 mole P205: (2+X)moles HF: (l-X) mole H2O in which X has any value in the range from 0 to1 inclusive, and then maintaining the reaction products in a closedvessel at a temperature and for a time sufficient to cause the reactionto go to completion according to the equation in which X represents anyvalue in said range.

10. The method of producing anhydrous monofluorophosphoric acid inconjunction with anhydrous difluorophosphoric acid which comprisesmixing phosphorus pentoxide and anhydrous hydrofluoric acidsubstantially in the ratio of 1 mole P205:3 moles HF, and thenmaintaining the reaction products in a closed vessel at a temperatureand for a time suflicient to cause the reaction to go to completionaccording to the equation P2O5+3HF=H2PO3F+HPO2F2.

11. The method of producing anhydrous monofiuorophosphoric acid whichcomprises mixing phosphorus pentoxide and an aqueous hydrofluonc acid ofabout 69%HF and maintaining the mixture in a closed vessel untilthereaction has gone to completion according to the equationP205+2HF+H20=2H2P03F.

12. That step in a method of producing anhydrous monofluorophosphoricacid which comprises mixing phosphorus pentoxide andan aqueoushydrofluoric acid of about 69% HP in a manner to prevent loss orreaction components or reaction products.

13. The method or producing anhydrous monofluorophosphoric acid whichcomprises mixing phosphorus pentoxide and an aqueous hydrofluoric acidof about 69% HF in the ratio of 1 mole Pzm:2 moles HF:1 mole H20, andthen maintaining the mixture in a closed vessel until the reaction hasgone to completion according to the equation P:Os+2HI'+H20=2I-I:POaF.

14. The method of producing anhydrous monofiuoroph osphoric acid whichcomprises mixing phosphorus pentoxide and an aqueous hydrofluoric acidof about 69% HF in the ratio of 1 mole -P2O5:2 moles HFzl mole H2O,.andthen heating the product in a closed vessel at a temperature notexceeding about C. until the reaction has gone to completion accordingto the equation P205+2HF+H20=2H2PO3F.

15. The method of producing anhydrous difluorophosphoric acids whichcomprises mixing phosphorus pentoxide and anhydrous hydrofluoric acidand againtaining the resultant product in a closed vessel until thereaction has gone to completion substantially according to the equation16. The method. of producing anhydrous difluorophosphoric andmonofluorophosphoric acids which comprises mixing phosphorus pentoxideand anhydrous hydrofluoric acid, maintaining the resultant mixture in aclosed vessel until the reaction has gone to completion, substantiallyaccording to the equation and then separating the two acids in theresultant product by distillation.

17. The method of producing anhydrous difluorophosphoric andmonofluorophosphoric acids which comprises mixing phosphorus pentoxideand anhydrous hydrofluoric acid, maintaining the resultant mixture in aclosed vessel to thereby prevent the escape of reaction products untilthe reaction has gone to completion substantially according to theequation then distilling the resultant product to separate thedifluorophosphoric acid, in vapor form from the residualmonofluorophosphoric acid, and condensing the vapor.

18. The method of simultaneously producing anhydrous difluorophosphoricand monofluorophosphoric acids which includes the steps of mixingphosphorus pentoxide and anhydrous hydrofluoric acid in the ratio of lmole:3 moles, preventing the escape of reaction products from themixture until the reaction has gone to completion substantiallyaccording to the equation and then separating the difluorophosphoricacid in vapor form from the residual monofluorophosphoric acid bydistillation.

WILLY LANGE.

and monofluorophosphoric

